Bomber read al Qaeda magazine online

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That information could have changed the way the alert was handled, congressman says

Russia withheld details from U.S. officials about suspicions of Boston Marathon bombings suspect Tamerlan Tsarnaev in 2011, information that could have altered the course authorities followed, a U.S. law enforcement official told CNN.

While Russia did alert U.S. authorities about Tsarnaev's possible extremism, it kept out some facts, namely text messages referencing his desire to join a militant group, the source said.

However, sources told the Wall Street Journal that the United States also likely would have withheld such details for fear of divulging intelligence sources and methods.

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Last month, a U.S. official with knowledge of the investigation told CNN that Russia intercepted a communication between the mother of the accused Boston Marathon bombers and someone who may have been one of her sons "discussing jihad" in 2011. That source described the conversation as vague, and said that the Russians turned over the intercept to the FBI sometime during the last week of April.

House Intelligence Committee Chairman Mike Rogers, R-Michigan, told the Wall Street Journal that the withheld information could have changed the way U.S. officials worked.

Access to the texts "would have allowed the bureau to open an investigation where you could track (Tsarnaev's) communications," he said. "To me, that's where the ball really got dropped."

In 2011, Russian authorities alerted the United States to concerns that Tsarnaev was becoming increasingly radical. The Russians also raised questions about Tsarnaev's mother, Zubeidat Tsarnaev, according to several sources.

But the FBI found no evidence of extremist activity and closed the case. The names of both Tsarnaev and his mother were placed in a terror database, however.

Still, Tsarnaev was allowed to travel the next year to a restive Russian region rife with Islamist terror groups, and he returned to the United States after six mysterious months abroad.

Investigators have said they are looking at possible links between Tsarnaev and those groups during his time in the region.